The invention relates to the field of angstrom-level alignment and position, and in particular to angstrom-level alignment and position using an embedded coordinate system, without the use of alignment marks on the face of a wafer.
Previous forms of infrared alignment used conventional alignment marks, such as crosses and boxes, and were imaged with conventional optics. Resolution using conventional imaging techniques is limited to approximately λ/2. To view backside alignment marks, infrared illumination is required. At the longer, infrared wavelengths, resolution degrades, typically to 500 nm or more. In a special case, signal processing was applied to such low-resolution images to improve resolution in a 1000 nm-resolution infrared imaging system, signal processing techniques extended matching precision of a known pattern to infrared images within ˜100 nm, which is still insufficient for many applications.